The present invention relates generally to a photographic camera provided with an automatic light control and it relates more particularly to a camera adapted to accept any of film cartridges having structural signals differently configured according to the corresponding film speeds and capable of accepting, selectively, a photoflash unit with a predetermined high guide number and a photoflash unit with a predetermined low guide number and effecting an automatic guide number and film speed adjustment of the camera for flashbulb photography.
A photographic camera in which the mounting of a photoflash unit thereon for flashbulb photography sets the shutter speed to a predetermined value is known. In such a camera, exposure control for flashbulb photography is provided by an automatic diaphragm mechanism which adjusts the aperture in response to the operation of a focussing member. This automatic diaphragm mechanism is such that it provides a wide aperture when the focussing member is set somewhere in the `Distant` range and progressively narrower aperture as said member is shifted toward and past the `Close` range. However, even when the focussing member has been set to a given distance, if the photoflash unit mounted on the camera has a guide number different from that preset on the camera, proper exposure control is not provided unless the aperture setting is altered. To solve this problem, the conventional camera has been designed and constructed so that an adjusting member capable of adjusting the aperture is additionally provided in association with the automatic diaphragm mechanism, said additional adjusting member being actuatable by manipulating a guide number setting member located externally of the camera. Thus, before performing flashbulb photography, the photographer adjusts the aperture of the camera by operating the guide number setting member according to the photoflash unit employed. The automatic diaphragm mechanism also requires an aperture adjustment according to the speed rating of the film. Thus, since any automatic diaphragm mechanism is preset to a given film speed, the employment of a film with a speed higher than said given speed would result in over-exposure. It is for this reason that in the conventional camera, a second adjusting member is provided in association with the automatic diaphragm mechanism or the first mentioned adjusting member for adjusting the aperture setting, the second adjusting member being actuatable with a film speed setting member located externally of the camera.
In the conventional camera having the above construction however, before a suitable photographic performance can occur in flashbulb photography, the guide number and film speed setting members of the camera must be manipulated to adjust the built-in automatic diaphram mechanism to the particular photoflash unit and type of film employed. This arrangement is disadvantageous in that when the photographer is an amateur not skilled in the operation of the camera or due to simple improper manipulation, these setting operations are sometimes inadvertently omitted or erroneously performed, the outcome being a failure to achieve the proper exposure.
Furthermore, when the diaphragm mechanism is interposed between a lens system as is conventionally done, it is technically difficult to establish an integral relationship between the automatic diaphragm mechanism and each of the adjusting members and the assembly and positioning operations involved are highly time consuming. Another disadvantage is that the dimensional errors of the various component parts, when added together, cause an inability to attain an accurate exposure control.